1. Field of the Invention
The present invention relates to a technology for expanding dynamic range by combining images.
2. Description of the Related Art
Recently, a large number of imaging apparatuses, such as digital cameras, capable of recording a combined image by combining a plurality of images have been developed as products. Some of these imaging apparatuses have a function for ameliorating overexposure or dark portion noise by combining an image captured at a higher exposure with an image captured at a lower exposure than the exposure at which the brightness of an object is appropriate. This function is called a high dynamic range (HDR) function. Generally, the dynamic range of an image sensor is narrower than the dynamic range in the natural world. For example, when capturing a backlit scene, overexposure can occur.
When capturing an image at a lower exposure, since the overall image is dark, although overexposure can be suppressed, the impression of dark portion noise deteriorates. In contrast, when capturing an image at a higher exposure, since the overall image is bright, although the overexposure occurs, the impression of dark portion noise is ameliorated. With the high dynamic function, the overexposure and the impression of dark portion noise can be ameliorated by combining a plurality of images having low exposures and high exposures, with weighting given to the underexposed images for bright regions (overexposure etc.), and conversely, weighting given to overexposed images for dark regions.
When the object moves while capturing the plurality of images, the object can turn into a double image due to combining processing. Consequently, a technology has been discussed for suppressing double images in regions in which object movement has been detected by prohibiting combining processing. Generally, a region in which object movement was detected outputs a low exposure image. This is because for images captured at a high exposure, a moving object can exhibit overexposure.
Japanese Patent Application Laid-Open No. 2002-190983 discusses a technology that, for a region in which object movement was detected, outputs an underexposed image and weakens the strength of contour enhancement to suppress the object from turning into a double image and suppress amplification of the impression of noise in the underexposed image.
As described above, when combining a plurality of images, double images can be suppressed by prohibiting the combining processing for regions in which movement was detected and outputting the underexposed image as is. However, there is the problem that for a region in which movement was detected, when an underexposed image is output, the impression of noise in the region in which movement was detected deteriorates.
Although further deterioration in the impression of noise due to noise amplification in a region in which object movement was detected can be prevented by outputting an underexposed image and weakening the strength of contour enhancement like in Japanese Patent Application Laid-Open No. 2002-190983, it is difficult to ameliorate the impression of noise in the underexposed image that was originally there.